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Influences on crystal structure due to hydrogen bonding and other effects

Abstract

One of the most fundamental pieces of information available about a compound is the molecular structure, and one of the best methods for obtaining structural information for crystalline compound is to study the diffraction pattern obtained when the crystal interacts with an X-ray beam. The diffraction pattern can be analysed to give not only the molecular structure, but also information on the packing arrangements in the crystal, the 3-Dimensional crystal structure. This information on the molecular structure and packing within the crystal allow the study of weak intra and intermolecular interactions such as hydrogen bonds. In this project two different methods will be used to study hydrogen bonds. Firstly using a statistical approach, where one type of intramolecular hydrogen bond (the N-H...π bond between neighbouring residues on a peptide chain) is analysed using crystallographic data obtained from the Cambridge Structural Database. Secondly the diffraction data from a several very different compounds are solved and the resulting structures analysed in terms of molecular and crystal structure; how and why the molecules pack as they do in the crystal lattice, and influences of hydrogen bonds on this packing. The effect of changes in the molecular structure on the molecular packing and crystal structure is also considered by the analysis of diffraction data from several groups of compounds where there are small changes in molecular structure in going across the group. The effects considered are; the effect of changing a methyl group for a butyl group in the 1,3-dimethyl-2-imidazolidinone co-crystallised with methane-diphenol-3,5,3',5'-tetra'butyl, the effect of changing the methyl group for an amino or ethyl group in triphenylmethylphosphonium co-crystallised with p-tert-butylcalix[4]arene and finally the effect of changing the metal in the compounds M-bis(2,6-di(^t)butyl-4-methylphenoxy) bis(triphenylaminophosphonium) and M-bis(trimethylsilylamide) bis(triphenylmethylphosphonium), where M is an alkali earth metal.